It’s 2am, the stove has burnt the last of the wood we placed in it 2 hours ago and the temperature in our Lavvu has now dropped to around -7 degrees Celsius. My 4 buddies around me snore, toss and turn as we all enjoy a pretty interrupted night’s sleep in this very cold native tipi tent! We are on expedition on the IGO Adventures – N60 Norwegian Challenge.

As I lie here looking up at the canvas, I am cocooned in the Sea To Summit Spark Series III sleeping bag. This was the perfect opportunity to test this ‘best-in-class’ sleeping bag, and it was a piece of kit I was really keen to get my hands on and try out in the field !

So the Sea To Summit Spark (abbreviated to ‘Sp’) range comes in three different weights; there is the SpI (comfort rating +8 degrees, total weight 388g), the SpII (comfort rating of +2 degrees, total weight 513g) and the SpIII which I was testing, as this is their sub-zero and warmest option. The Spark range is their no frills and top range if your looking for weight vs warmth.

Details

In terms of weight the SpIII really is a bantamweight bag coming in at a total of 690g. But don’t be decided – it packs a real punch keeping you comfortably warm down to -4 degrees (with extreme rating of -20 degrees). Filled with 850+ loft down (98% goose) which itself weighs 400g, this difference of just 290g demonstrates a huge attention to detail ensuring all additional components and materials of the bag are second to none. Frills and excess features are minimal – it has a one directional 1/3 length zip and one toggle at the head area to allow you to cocoon yourself – and that’s literally it! The result is that the SpIII is one of the best warmth for weight minimalists sleeping bags money can buy. This is the raison d’etre of the SpIII; it’s super capable and light and you can feasibly take it on a lightweight run / trek no problem.

Here are the quick stats of the SpIII ‘long’ which I was testing:

• Price: £450 (from Sea to Summit website)
• Weight: 690g (nb this is the total weight of the bag, and this is for the ‘long’ version, the ‘regular’ version weighs 625g)
• Temperature Rating: comfort -4 degrees, extreme -20 degrees
• Zip: Left 1/3 length zip
• Fill: 400g of ULTRA-DRY Down 850+ Loft Water resistant down (comprised of 98% goose down and 2 % duck down)
• Compression volume: 3.7L (the size it would occupy in your bag when in it’s fully compresses stuff sack – it’s not hungry!)
• Seasons: Spring/Autumn/Winter
• Uses: Ideal for travel, adventure racing, and ultra lightweight hiking and alpine climbing

contoured hood with draw-cord

1/3 length zip on the left hand side

Warmth

Despite its compact and lightweight nature, the SpIII is warm, and as soon as you slide your way into it, you can tell the insulation is there. Whilst testing this in Norway, the temperature at the coldest point of the night would push well beyond the stated ‘comfort zone’ of the SpIII (-4 degrees), as we were experiencing some quite harsh weather. So I pimped up the warmth factor by utilising the Thermolite Reactor Compact Plus (263g, £55); a really great sleeping bag liner, to make sure I kept toasty. It is advertised to add up to 11 degrees of additional warmth – although it is kind of hard for one to quantify this outside of a laboratory, it noticeably kept me warmer and I was really really grateful to have it. Also, in milder summer months, I think this liner would in itself be all you need to sleep in – so a good and practical purchase too with scope to use in a multitude of scenarios and seasons year round.

The sleeping bag in its stuff sack – pretty small!!

This is the storage sack “expandable shell” which is really neat and to be used for storage when you’re not using it

You get a really neat envelope with these certification documents in – real nice touch, and great to have the detailed info to hand

Attached to the base of the sleeping bag, detailing the sleeping bag unique number and grooving it adheres to the qualities it advertises

Fit

I am 6’2″ (188cm) and actually found the length absolutely fine and adequate. On reading some other reviews, I note there was the odd comment of it being a bit restricted or short, but I really didn’t find this the case at all. Admittedly I am a fairly slight build (68kg), but the dimensions were really good for me, including around the torso area too. The 1/3 length zip is of course less flexible in terms of providing varied ventilation, to your feet for example, but again, I didn’t miss this feature at all – and when the emphasis on the design of an article is weight, as with the SpIII, it would be a great shame to go to all those lengths and then needlessly add around 50+grams to the weight for a needless zip.

It has a contoured hood with a draw-cord which you can tighten right up to cover most of your head and just leave a small area to breath through (as I did in Norway on this trip!!), helping preserve more valuable heat!

The sleeping bag stuffs into a small compressions sack which you can compress even further still with 4 toggles. It also comes with a larger storage sack (which they call an ‘expandable Storage Cell’), and this will help prolong the life of the bag by preserving the down loft and its insulation properties.

Conclusion

I was super impressed with this sleeping bag. Admittedly, the price tag is very steep, so it depends on what importance you place on lightweight and optimum performance, and if you can justify it. If money wasn’t too much of a concern – this bag would be my choice. Looked after properly, you should get years of use out of this which perhaps makes it easier to reconcile the spend too. This is a great bit of kit and I’m stoked to have it as my sleeping bag of choice in my kit, and for sure I’ll be using this on many more hikes, expeditions, adventures and races to come.

Sea To Summit Spark SpIII Sleeping Bag